Simple redirect function to correctly redirect lost posts.

redirect-lost-posts.php

<?php
/**
 * Redirect Lost Posts
 *
 * @author Justin Kopepasah <justin@kopepasah.com>
 * @license MIT
 */
add_action( 'template_redirect', function() {
	// Only redirect if nothing is found.
	if ( is_404() ) {
		$post = get_page_by_path( $_SERVER['REQUEST_URI'], OBJECT, 'post' );

		// Only redirect if a post is found using the URI.
		if ( null !== $post ) {
			wp_safe_redirect( get_permalink( $post->ID ), 301 );
			exit();
		}
	}
} );